The flexibility of communication networks based on light signals conducted via optical fibres is greatly increased by the availability of optical fibre-compatible optical components such as circulators, switches and tuneable filters. Optical circulators enable light signals to be routed from one optical fibre to another. Optical switches enable light signals to be selectively transmitted via one or more optical fibres. Optical add, drop, and add-drop filters enable light signals at different optical frequencies to be selectively transmitted and received via an optical fibre.
Conventional optical components of the types discussed above are made of discrete optical elements. As a result, such optical components are bulky and expensive. A substantial portion of the cost of making such optical components arises because the elements of such components are physically large and have to be individually and precisely aligned relative to one another. For example, a recent catalog published by the Fuji Electrochemical Corporation, Tokyo, Japan shows a Model YC-115A four-port optical circulator with dimensions of 43.times.30.times.8 mm, excluding the optical fibre connectors. A Model YS-111A 2.times.2 optical switch has dimensions of 50.times.43.times.8 mm, excluding the optical fibre connectors. The large size of these components limits the density with which optical fibre switching systems can be built.
To further increase the flexibility of communication networks based on light signals conducted via optical fibres, it is necessary to increase the density with which optical fibre switching systems can be built, and to reduce substantially the cost of the optical components used in such switching systems.